I'm a geochemist. In the past ten years I've fixed mass spectrometers, blasted sapphires with a laser beam, explored for uranium in a nature reserve, and measured growth patterns in fish ears, and helped design the next generation of the world's most advanced ion probe. My main interest is in-situ mass spectrometry, but I have a soft spot in my heart for thermodynamics, drillers, and cosmochemistry.

Friday, April 05, 2013

In the aftermath of the Chelyabinsk fireball last month, there have
been increasing calls to identify asteroids on a collision course with Earth
and develop technologies to deflect them.
This would be a very stupid thing to do.

The reason for this can be seen in figure 1, below. In part A, this figure shows the minimum
deflection necessary to make an asteroid on a collision course with Earth to miss. The deflection angle depends on how far from
Earth this deflection occurs; the farther away, the smaller the angle. In practice, very small angles from very far
away would be used.

The green line shows the minimum translational distance an
asteroid must be deflected in order to miss the Earth.

Figure 1. An illustration for how the deflection needed to make an asteroid miss can be used to make many more hit.

The problem with such a system is shown in part B of the
figure. Here, an identical deflection is
applied to a harmless asteroid that never would have hit Earth. However, by deflecting it towards the Earth,
this harmless rock ends up exploding in the atmosphere. For a rock the size of the Chelyabinsk bolide, this is similar in force
to a large nuclear weapon.

The area of the red circle- the smallest radius necessary to
protect the earth- is three times the cross section of the earth. So for every rock you deflect, there will be at least three harmless rocks that can be turned into weapons of mass destruction. By definition, a “planetary defense system”
turns every rock that passes close to the Earth into a potential weapon of mass destruction.

Who would actually crash a space rock into a populated area
of the Earth? The same people who crash
airplanes into skyscrapers of course.
And while only a few rouge countries can launch satellites, any
spacecraft in radio contact with Earth can potentially be hijacked by a hacker
on Earth with enough chicken wire to erect a makeshift dish in a desert. Amateurs already pick up signals from our most distant space probes; an asteroid deflection mission would be a magnet for
every doomsday cult, terrorist fanatic, delusional hacker, and other misanthropes whose imagination had previously been limited to shooting up schools. Obviously nobody is going to design a space
deflector to be hackable, but then the drone the Iranians hijacked wasn’t
supposed to be vulnerable to those sorts of attacks either.

The threat of an asteroid impact is miniscule. More people were killed in floods this week
than were killed by impacts in the known history of the human race. A quick glance at the morphology of our
planet will explain why. Even the
giant extinction-causing impacts are less common than large flood basalt
eruptions of similar ecological lethality.
But developing the technology to deflect asteroids potentially gives all
the wrong people access to a weapon the size of a large hydrogen bomb for a
fraction of the development cost. This is not a smart thing to do.

Disclaimer:

All opinions, measurements, figures, and facts on this page are the personal opinions of Charles W. Magee, Jr, and do not represent the views of any of his employers: past, present, present-but-about-to-be-past, or future. None of the content herein has been subject to peer review, and should be treated with caution or derision. Any passing mention of OSHA code violations, criminal activities, unethical or unscientific behavior, or the clandestine Australian nuclear weapons program are fictions created to make rhetorical points, and do not represent the reality of my, or anyone else's, workplace. Do not attempt any scientific protocols described herein at home, with the exception of the chocolate chip cookie recipe. Do not apply the products of that protocol to individuals with heart disease, diabetes, high blood pressure or cholesterol, egg, wheat, dairy, or chocolate allergies. Do not view this blog continuously for more than 45 minutes without stretching and taking other precautions to prevent computer-related chronic injury.
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